Hermetic high-speed turbo generators are known, in which the hermetic property is based on the fact that the turbine, the generator and preferably also the feed pump are arranged on the same shaft and within a common casing, wherein external leaks e.g. from rotary shaft seals are avoided and only internal leaks between said different components are possible; in other words, the turbo generator is externally hermetic. One known turbo generator is disclosed in patent publication FI 66234, whereby the device is used to convert thermal energy into electric energy. The circulating medium used in the process is vaporized in a thermal boiler, from which it is led into a turbine, in which it expands, and further into a condenser. The turbine rotates the generator to generate a high-frequency current by a method known from e.g. asynchronous electric machines. From the condenser, the circulating medium is led into a feed pump and further back into the boiler. The operation of another known turbo generator is presented in the application publication FI 904720, in which the bearing system of the turbo generator also applies said circulating medium as a lubricant.
Into the casing of the turbo generator must be introduced the high-temperature, vaporized circulating medium from the boiler or the like and the cooled circulated medium from the condenser. Furthermore, the expanded circulated medium must be led through the casing from the turbine into a recuperator or directly into the condenser. The boiler, the condenser and the recuperator are devices separate from the turbo generator, and the connections are normally implemented with pipes. The turbo generator normally comprises a circular end flange, through which the circulating medium is led and which is fixed by a bolted joint to the cylindrical casing. The end flange, in turn, is equipped with the necessary pipe connections for fixing the pipes with e.g. a threading. For absolute tightness, the pipes are often connected to each other by welding.
A problem in the end flange is particularly the tightness of the flange joint. According to the publication by Larjola J., Lindgren O., Vakkilainen E., “Sähköä hukkalämmöstä”, publ. No. D:194, 1991, Ministry of Trade and Industry, Department of Energy, Helsinki, it has also been found in practice that particularly the inlet of the vaporized circulating medium tends to leak, which is due to the thermal movement which is a problem known as such in power plant technology. In the turbo generator, said thermal movement particularly affects hot lead-in ducts of the vaporized and expanded circulating medium.
The hermetic feature is particularly important when the circulating medium used is other than water and when the power of the turbo generator is low, so that a leak would not cause considerable costs and power losses. According to the article by Jokinen T., Larjola J., Mikhaltsev I., “Power Unit for Research Submersible”, proceedings of te International conference on electric ship, Istanbul, 1st September 1998, p. 114-118, the hermetic feature is particularly important under special conditions in which a leak could cause a damage of the equipment itself.
It is also known that the flange joint or other lead-in ducts and leakages are sealed with a welded joint, but it is then obvious that this makes the releasing, re-mounting and maintenance of the turbo generator considerably more difficult.